The present invention relates generally to an apparatus for synchronizing the movement of glass sheets in a heat treating operation, and more particularly, concerns an apparatus for synchronizing the movement of glass sheets into a furnace such that any distortion pattern formed will be identical on all sheets.
In the known methods of making and forming glass, defects may inadvertently be produced in the glass which render the glass optically imperfect. Defects may also be produced in the glass during subsequent manufacturing operations such as during heat treatment or thermal conditioning in a bending and/or heat strengthening operation, for example. Among the optical imperfections that may be produced is surface distortion. Surface distortion, as the term is used herein, generally refers to variations in surface flatness, i.e., concave and convex portions.
Surface distortion in glass causes the glass surface to reflect a distorted image. For example, convex portions shrink the image and concave portions magnify the image. When a pair of glass sheets having surface distortion are formed into a laminated structure, such as an automobile windshield, and any convex and concave portions do not match or coincide, portions of the facing surfaces will be spaced farther apart than other portions. These variations in spacing tend to produce optical distortion which becomes more pronounced when the windshield is mounted at an angle to the vertical in an automobile.